Actuator driver with open-circuit and stray ground protection

Abstract

Actuators typically include one or more coils which are driven by a current source to effect positioning of a movable member. However, faults can occur wherein a conductor connecting the coil to the current source is open circuited or short circuited to ground. This can lead to a loss of control over the actuator, in turn creating a potentially dangerous condition. In order to overcome this problem, an actuator driver circuit according to the present invention includes a first current source for generating a first current at an output terminal thereof, a second current source for generating a second current at an output terminal thereof and first and second actuator coils connected in parallel between the output terminals of the first and second current sources. The current sources are controlled so that at least one of the current sources is capable of generating current for the coils even in the event of an open or short circuit fault condition.

I claim: 
     
       1. An actuator driver circuit for controlling an actuator having a pair of parallel connected coils, comprising: a first current source for generating a first current of a first polarity at an output terminal thereof;   the parallel connected coils including first and second common ends, the first common end being connected to the output terminal of the first current source; and   a second current source for generating a second current of a second polarity opposite the first polarity at an output terminal thereof, the second common end of the parallel connected coils being connected to the output terminal of the second current source such that the currents generated by the first and second current sources flow in the same direction through the parallel connected coils.   
     
     
       2. The driver circuit of claim 1, wherein each current source comprises an operational amplifier which receives first and second power supply input voltages. 
     
     
       3. The driver circuit of claim 2, wherein the first and second power supply voltages define a range of voltages includes ground potential. 
     
     
       4. The driver circuit of claim 2, further including an isolated power supply for developing the first and second power supply voltages. 
     
     
       5. The driver circuit of claim 2, further including a power supply for developing the first and second power supply voltages wherein the first power supply voltage is a non-ground potential and the second power supply voltage is at ground potential. 
     
     
       6. The driver circuit of claim 2, further including a power supply for developing the first and second power supply voltages wherein the power supply voltages are of opposite sign and equal magnitude. 
     
     
       7. An actuator driver circuit for controlling an actuator having a pair of parallel connected coils, comprising: a first current source for generating a first current at an output terminal thereof;   a second current source for generating a second current at an output terminal thereof;   the parallel connected coils including first and second common ends separately connected to the output terminals of the first and second current sources, respectively; and   means for providing first and second different power supply voltages to the first and second current sources, the first and second power supply voltages defining a range of voltages which includes ground potential, whereby at least one of the current sources is capable of generating current for the coils even in the event of a fault condition.   
     
     
       8. The circuit of claim 7, wherein the first power supply voltage is a non-ground potential and the second power supply voltage is at ground potential. 
     
     
       9. The circuit of claim 8, wherein the first and second current sources each include an operational amplifier. 
     
     
       10. The circuit of claim 8, wherein the direction of the current generated by each current source is controlled by a control voltage. 
     
     
       11. The circuit of claim 7, wherein the first power supply voltage is a positive potential and the second power supply voltage is a negative potential. 
     
     
       12. The circuit of claim 11, wherein the first and second power supply voltages are of equal magnitude. 
     
     
       13. The circuit of claim 12, wherein the first and second current sources each include an operational amplifier. 
     
     
       14. The circuit of claim 12, wherein the direction of the current generated by each current source is controlled by a control voltage. 
     
     
       15. An actuator driver circuit for controlling an actuator having a pair of parallel connected coils, comprising: a first current source for generating a first current at an output terminal thereof;   a second current source for generating a second current at an output terminal thereof;   the parallel connected coils including first and second common ends separately connected to the output terminals of the first and second current sources, respectively; and   means for providing first and second different isolated voltages to the first and second current sources whereby at least one of the current sources is capable of generating current for the coils even in the event of a fault condition.   
     
     
       16. The driver circuit of claim 15, wherein each of the first and second current sources includes an operational amplifier which receives the isolated voltages. 
     
     
       17. The driver circuit of claim 16, wherein the direction of current generated by each current source is controlled by a control voltage coupled to control inputs of the operational amplifier.